Vitamin D, often called the “sunshine vitamin,” is essential for bone health, immune function, and calcium regulation. In recent years, interest has grown in its potential role in male reproductive health, particularly its influence on

testosterone—the primary male sex hormone responsible for muscle mass, energy, libido, and overall vitality. Vitamin D receptors (VDRs) and metabolizing enzymes are present in testicular cells (Leydig cells), suggesting a biological basis for interaction. Observational studies frequently link higher serum vitamin D levels (measured as 25-hydroxyvitamin D [25(OH)D]) to elevated testosterone, especially in deficient individuals. However, whether supplementation causally increases testosterone remains debated, with mixed results from randomized controlled trials (RCTs) and meta-analyses.This report synthesizes recent evidence (primarily 2023–2025), highlighting positive associations, supplementation effects, and limitations.

Observational Evidence: A Consistent Positive Correlation

Cross-sectional and correlational studies often report that men with higher vitamin D status have higher total testosterone, free testosterone, or bioavailable testosterone. This pattern appears stronger in deficient populations (e.g., <50 nmol/L or <20 ng/mL), older men, obese individuals, or those with metabolic issues.

• Deficiency is associated with lower testosterone in adult males, with some reviews noting potential causal links via genetic or mechanistic pathways.
• In healthy or specific cohorts (e.g., young men, military personnel), positive correlations persist, though not always strong or universal.
• Emerging reviews emphasize vitamin D’s role in male reproductive health, including testosterone production through receptors in testicular tissue.

These associations are biologically plausible: vitamin D influences gene expression in Leydig cells, potentially supporting androgen synthesis. However, observational data cannot prove causation—confounders like obesity (which lowers both vitamin D and testosterone), age, sun exposure, and lifestyle play roles.

Intervention Studies: Supplementation Effects on Testosterone

RCTs provide stronger causal evidence, but results vary widely.A key 2024 meta-analysis of 17 RCTs (1,774 adult men) found that vitamin D supplementation significantly increased total testosterone (weighted mean difference [WMD] 0.38 nmol/L, 95% CI 0.06–0.70). Subgroup analyses showed stronger effects with:

• Doses >4,000 IU/day
• Durations >12 weeks
• Older adults

No significant changes occurred in free testosterone, luteinizing hormone (LH), follicle-stimulating hormone (FSH), sex hormone-binding globulin (SHBG), free androgen index (FAI), or estradiol.Earlier foundational RCTs (e.g., 2011) reported increases in total, bioactive, and free testosterone with high-dose supplementation (e.g., 3,332 IU daily for 1 year) in deficient, overweight men. Some mechanistic studies support direct effects on testicular testosterone production.Conversely, many RCTs show no benefit:

• In healthy men with normal baseline levels, supplementation (e.g., 20,000 IU weekly for 12 weeks) had no effect on total testosterone, though it influenced insulin sensitivity.
• Systematic reviews (2023) describe effects as inconclusive, with limited changes in total testosterone but possible impacts on SHBG or free testosterone.
• In infertile men (2025 meta-analysis), vitamin D3 increased sperm parameters (count and motility) but not significantly androgen levels.

A 2023 systematic review concluded supplementation effects remain inconclusive overall, calling for longer-term, diverse RCTs.

Key Moderating Factors and Mechanisms

Benefits appear context-dependent:

• Baseline deficiency — Stronger responses in men with low 25(OH)D (<50 nmol/L).
• Dose and duration — Higher doses and longer interventions yield better results in positive meta-analyses.
• Population — More evident in older, deficient, obese, or hypogonadal men; minimal in young, healthy, sufficient individuals.
• Confounders — BMI, age, and comorbidities often mediate outcomes.

Mechanistically, vitamin D may enhance testosterone via:

• Direct action on Leydig cells
• Improved insulin sensitivity (indirectly supporting hormones)
• Anti-inflammatory effects

However, excessive supplementation risks hypercalcemia or other issues, so monitoring is essential.

Criticisms and Mainstream View

While some data suggest modest boosts (especially total testosterone under optimal conditions), many high-quality RCTs find no meaningful increase, particularly in non-deficient men. Critics highlight heterogeneity in studies (dosing, populations, durations) and potential publication bias. Mainstream endocrinology does not recommend vitamin D supplementation primarily for testosterone enhancement—it’s better established for deficiency correction, bone health, and immunity.Ongoing trials (e.g., acute effects in women, though less relevant here) may clarify further.

The evidence for vitamin D increasing testosterone is promising but not definitive. Observational links are strong, and a recent major meta-analysis supports modest increases in total testosterone from supplementation in men—particularly with higher doses, longer durations, and in deficient or older populations. However, many RCTs show no effect, especially in healthy men with adequate levels. Vitamin D optimization remains worthwhile for overall health, but it’s not a reliable standalone “testosterone booster.” Men concerned about low testosterone should test both vitamin D and hormone levels and consult a healthcare provider for personalized guidance, as individual factors heavily influence outcomes.

Citations

Additional sources: PubMed-indexed studies on vitamin D3 in infertile men (2025 meta-analysis); Frontiers review on vitamin D in male sexual functions (2025)

Abu-Zaid A, et al. (2024). The Impact of Vitamin D on Androgens and Anabolic Steroids among Adult Males: A Meta-Analytic Review. Diseases, 12(10):228. doi:10.3390/diseases12100228

Monson NR, et al. (2023). Association Between Vitamin D Deficiency and Testosterone Levels in Adult Males: A Systematic Review. Cureus, 15(9):e45856. doi:10.7759/cureus.45856

Various RCTs and reviews referenced in the above meta-analyses (e.g., Pilz et al., 2011; Lerchbaum et al., multiple years)